The present invention relates to a device for holding a drum on one side, particularly in a printer or copier, with an inner ring established on a shaft concentric to the drum, and with an outer ring that carries an end-face of the drum on a shoulder. The present invention also relates to a method using the aforesaid device.
An important instance of using the present invention concerns the holding of a drum that has a cladding layer, upon which a toner image can be produced for printing or copying. The cladding layer can be a photoconductive layer or a magneto-optically influenced layer. Such a drum must be free of play and be securely fixed in a bearing device over the entire temperature range of the use.
When operating the drum, different expansions of shaft and drum can result by means of local temperature differences. For example, great expansion differences result when the shaft is expediently fabricated of steel and the drum out of aluminum. If the drum is in a cold state and is installed in a printer not yet warmed up, then different expansions of the drum and shaft can thereby occur in the warmup phase. For customary dimensions, the differences in expansion can be noticeably greater than 0.1 mm. The holding element, which bears the drum on one side, must then recede by this expansion difference since the forces produced as a result of the thermal expansion are very great. When the printer and consequently the drum cool off in turn, e.g. after shutdown, the drum generally shrinks more severely than the shaftxe2x80x94the result is a process the reverse of that during warmup. It can happen that the holding element that holds the drum on one side does not participate in the receding movement of the drum in the axial direction, e.g. because the device with the holding element migrated during the thermal expansion the shaft, and a potentially available restoring force is not adequate to exact the reverse movement, especially then when spread elements, that spread out upon screwing, are present for the exact centering of the drum flange on the drive shaft between the drive shaft and the drum flange. The result thereof is that the end-face of he device lies loosely - a tilted, out of round running of the drum can occur. Theoretically, it would be possible to allow a restoring force to act on the device that is so great that the device on the shaft also does the receding movement during the cool down. However, this restoring force must be extremely great which leads to a high technical expenditure. If a tight fit is used for the exact centering of the drum flange on the drive shaft instead of the spread elements, a tilting and thus a jamming of the device is probable.
A bearing means free of play is known from the EP-A-0 345 270 for a photoconductor drum in a printer or copier. The photoconductor drum disclosed therein is arranged fixed on one side of the drive shaft. The other free end of the drum is held by an hub flange that can be moved in an axial direction. A clamp mechanism presses resiliently against the drum. For the centering of the drum flange on the drive shaft, spread elements which spread during screwing are arranged between the drive shaft and the drum hub flange. In this fashion, a high precision of balanced running is to be achieved given easier replacement of the photoconductor drum.
A fastening means for a photoconductor drum of an electrographic printer or copier is known from DE-A43 15 274. The photoconductor drum is clamped between the two drum flanges, whereby one drum flange is held (detachably) on the shaft with the aid of an adjusting nut that can be screwed onto the shaft. A compression spring is active between the drum flange and the adjusting nut, which presses one of the drum flanges against the drum. The adjusting nut and the associated drum flange are joined together in a detachable fashion with the aid of a clamp part.
The two above recited publications are based on the developments of the same applicant. The content of the two publications is hereby incorporated by reference in the present patent application.
A device for holding a drum on one side in a printer or copier is known from the JP 03-181 983 A with abstract, whereby the drum in the holding state is supported by the shoulder of an outer ring. This outer ring is arranged (such that it can be shifted axially) on an inner ring that is arranged on a shaft running concentric to the drum axis. This inner ring is moveable in an axial direction and supported against a spring. In this fashion, the outer ring in rigid connection with the inner ring is elastically pressed against the rim of the photoconductor drum in the holding state of the photoconductor drum.
The JP 62-67580 with abstract discloses a holding device for holding a photoconductor drum. A conical bevel of the photoconductor drum is held by a conical counterpart of a ring bearing. The ring bearing is freely moveable on a shaft in an axial direction and is pressed against the photoconductor drum by means of a spring.
The publications JP 01-254971 with abstract and JP 05-289588 A with abstract also concern holdings for photoconductor drums. The respective elements for holding an end section of the photoconductor drum are arranged on the concentric shaft and movable in an axial direction.
An object of the present invention is to indicate a device and a method for holding a drum on one side, said device, or respectively, said method enabling the drum to be securely clamped free from play over the entire operational temperature range.
In an embodiment, the present invention provides a device for holding a drum for a printer or a copier on one end of the drum. The device comprises an inner ring connected to a shaft that is concentric to the drum The device further comprises an outer ring that comprises a shoulder. The shoulder of the outer ring engages the end of the drum. The outer ring is connected to the inner ring by an elastic element. The outer ring is axially shiftable relative to the inner ring thereby enabling the shoulder of the outer ring to press against the end of the drum in a holding state.
In an embodiment, the elastic element comprises a disk-shaped spring.
In an embodiment, the disk-shaped spring comprises a star-shaped spring having spring lamellas arranged in a Meander form.
In an embodiment, the shoulder of the outer ring has a convex surface and the end of the drum is tensed concentrically to the shaft in the holding state.
In an embodiment, the device further comprises a shifting element that frictionally connects the inner ring to the shaft in a first shifted state. The shifting element also flexibly releases the inner ring from the shaft in a second shifted state.
In an embodiment, the shifting element is a rotary knob that is threadably connected to the shaft.
In an embodiment, the device further comprises a detent motion device that engages the rotary knob and which restrains axial movement of the rotary knob.
In an embodiment, the star-shaped spring is tensed using a prescribed spring force in a detent state and play is present between the flange and the outer ring or, in other words, the flange is spaced-apart from the outer ring.
In an embodiment, the shaft and the drum have different thermal expansion coefficients.
In an embodiment, the shaft comprises steel and the drum comprises aluminum.
In an embodiment, a spring path in the holding state is a multiple of the expansion coefficient difference of the shaft and the drum that arises during operation of the drum.
In an embodiment, the inner ring comprises a first sleeve connected to the shaft and a second sleeve that can be shifted axially. The first and second sleeves are disposed between the shaft and a bearing bush which is disposed between the first and second sleeves and the inner ring.
In an embodiment, the device further comprises a radial tension element disposed between the first sleeve and the second sleeve. The radial tension element radially aligns the bearing bush concentric to the shaft in an extended state.
In an embodiment, the radial tension element is a star-shaped spring that radially elongates against the first sleeve given pressure of the second sleeve and which concentrically aligns the bearing bush on the first and second sleeves.
In an embodiment, the second sleeve comprises a detent motion device against which the shifting element stops in the holding state and which biases the second sleeve against the first sleeve under compression of the radial tension element.
In an embodiment, the spring elements of the star-shaped spring are connected to the inner ring and the outer ring with screws.
In an embodiment, the star-shaped spring is connected to the inner ring, the outer ring and the flange with screws.
In an embodiment, the outer ring is releasably connected to the flange.
In an embodiment, the present invention provides a method for holding a drum on one end of the drum that comprises the steps of providing an inner ring connected to a shaft that is concentric to the drum and an outer ring that comprises a shoulder that engages the drum and whereby the outer ring is connected to the inner ring by an elastic element and further whereby the outer ring is axially shiftable relative to the inner ring thereby enabling the shoulder of the outer ring to press against the end of the drum in a holding state, shifting the outer ring axially relative to the inner ring during operation of the drum and the shaft and pressing the outer ring in a holding state against the end of the drum by means of the elastic element.
In conformity with the invention, the device contains an inner ring established on the shaft as well as an outer ring that bears an end-face of the drum on a shoulder. The outer ring is axially adjustable relative to the inner ring. In the state in which the drum is held by the device, an elastic element presses the outer ring against the end-face of the drum, whereby the elastic element is supported on the inner ring. Whenever different expansions of the drum and shaft occur as a result of temperature changes, these expansions are thereby intercepted by the elastic element, whereby an axial shift occurs between the outer and inner ring. Thus, the forces acting during the thermal expansion are safely intercepted by the elastic element. Whenever a cool down of the drum and the shaft takes place after an expansion, the elastic element acts such that the outer ring follows the longitudinal shrinkage of the drum, whereby the clamping force onto the end-face of the drum is maintained. A loosening of the clamping of the drum at the outer ring is avoided. As a result thereof, the drum remains, in all temperature conditions, in a defined, concentric position to the shaft - an out of round or tilted running of the drum is avoided.
A method for holding a drum on one side is indicated according to further aspect of the invention. The advantageous effects already described in connection with the device are achieved with the aid of this method.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.